Author Topic: Engine Rebuild! (Read 4506 times)

Scumball · « **on:** February 27, 2007, 04:56:41 AM »

Hi folks!

Just bought a 160k engine for rebuild, while I continue running mine into the ground... The rebuild is to be done on a reasonably tight budget, so I'm after some advice on the best way to eke out a few more BHP without blowing the bank manager. (Take that as you will!)

My initial thought is to use M44 pistons, which I'm told are the same pin > deck, and differ only in Bore... Is this right? Adding a few more cubes is always going to be good for power, but I don't have the knowledge, funds or experience to start messing with strange combinations of cranks, rods and pistons.

If the M44 pistons can be used, I'll then be looking at a higher CR because of the increased "squish" area, right? I'm thinking that if the CR isn't too high at this point, a small skim to raise the CR up to about 11:1 would be the best way to release all those ponies.

That's my initial gambit anyway... Tell me what you experts think, and we'll discuss further.

Cheers,

Omi

StreetSpec_iS · « **Reply #1 on:** February 27, 2007, 09:54:19 PM »

as i said on the Zone. overbored m44 bottom end with custom pistons. gets to preety much 2000cc. theres a few boys on here building that spec now.

would prob release a few hounds. with some nice cams and a 7000+ rpm chip and maf would be nice.

2002maniac · « **Reply #2 on:** February 28, 2007, 07:21:54 AM »

Check out my thread

http://www.m42club.com/forums/showthread.php?t=160

I'm essentially doing the same thing Streetspec_IS mentioned.

M44 crank with modified S52 pistons. Really isnt costing me much more than a stock rebuild

I dont know what you can do about pistons since the S52 wasnt offered overseas.

Custom would be nice, but you might have to blow your banker

A complete M44 bottom end wouldnt be bad...

1991 E30 M42 · « **Reply #3 on:** February 28, 2007, 04:22:19 PM »

I'm rebuilding an engine right now with M44 crank, rods, and .50 over pistons, with all of that, the displacement comes out to about 2.1L

cecotto · « **Reply #4 on:** February 28, 2007, 07:13:27 PM »

Quote from: 1991 E30 M42;20307

I'm rebuilding an engine right now with M44 crank, rods, and .50 over pistons, with all of that, the displacement comes out to about 2.1L

Are you sure you got your math right ?

The M44 crank is 83.50mm, this would mean you would need a bore of ~89.50 to get 2.1L. Thats a 5.5mm overbore compared to standard.

asubimmer · « **Reply #5 on:** February 28, 2007, 07:18:20 PM »

so what do we need to use s50/52 pistons? Do you have to use the m44 crank w/ the m42 connecting rods?

1991 E30 M42 · « **Reply #6 on:** February 28, 2007, 09:23:30 PM »

Quote from: cecotto;20320

Are you sure you got your math right ?

The M44 crank is 83.50mm, this would mean you would need a bore of ~89.50 to get 2.1L. Thats a 5.5mm overbore compared to standard.

I did that in my head, it actually comes out to:
pi 42.7425^2 x 83.5 x 4 = 1916973.813 cubic millimeters = 1916.973813 cubic centimeters
thats with a 85.485MM bore and a 83.50MM stroke

franz · « **Reply #7 on:** March 01, 2007, 11:02:00 PM »

i think in order to get it up to 2.1l u need a m47 crank

Massimo · « **Reply #8 on:** March 04, 2007, 11:14:54 PM »

Well Dont forget that if you are over boaring you are going to loose pressure in the cylinder. So you have to increase the displacement, to mantain the pressure, if you want an 11:1 compression. You could do a cheaper alternative when it comes to your crank. I bought a book called Step by Step Guide to Engine Blue Printing. Its written with the experties of pro nascar , and drag engine builders from the states. Its based on chevy V8s but the same principals apply to any engine. Basically what they were doing, is taking the crank, then welding up (i dont know what it is called but the point where the rods connect to the crand) so that they can regrind it offset. Therefore giving a few more millimeters of displacment to each stroke. I know it sounds a bit dogg but if they are doing it on 600hp v8s then im shore a forged crank can take it. Here is a drawing to help its a cross section of a crank

StreetSpec_iS · « **Reply #9 on:** March 04, 2007, 11:17:32 PM »

hey Mass, good to see you here.

Offset grinding was big back in the day, esp with Chryslers. id be interested to know how the m42/44 would take to it.

Massimo · « **Reply #10 on:** March 04, 2007, 11:27:00 PM »

Cheers mate cant wait for this crusie to happen so we can meet. But yeh i recon wit a forged crank it should be good id love to try it my self. wonder how much of a gain id get!!!

Scumball · « **Reply #11 on:** March 05, 2007, 04:33:23 AM »

The engine goes to the engineers this weekend... He'll pull it apart and see what is needed. Will post back here with the results.

I'm thinking a standard rebuild using orginal everything, just balanced and fresh bearings as appropriate... Then RaceTEP can supply me with a set of JE pistons to take care of a displacement increase (bigger bore) and they can deal with CR at the same time. Maybe get something like 10.8:1 compression when I order the pistons, and take up the slack with a gentle skim to the head?

Don't wanna go insane on this motor, as I've plans for an all-singing, all-dancing FI project when I've got the old engine out and on the bench.

Author Topic: Engine Rebuild! (Read 4506 times)

franz